1. Field of the Invention
The present invention relates to an air-cooled oil-free screw compressor in which lubricating oil is air-cooled.
2. Description of the Prior Art
In the past, an air-cooled oil-free screw compressor shown in FIG. 2 has been well known, which comprises a first stage compressor body 12 and a second stage compressor body 13, each of which encases therein a pair of male and female screw rotors 11 meshed with each other, and a gear box 14 which encases therein a gear for transmitting a driving force of a motor not shown to each screw rotor 11 to increase speed. There is further provided a cooling water circulating flowpassage 19 which extends from a cooling jacket 15 provided within the compressor body 12 to a cooling jacket 16 provided within the compressor body 13 and returning to the cooling jacket 15 via a water heat exchanger 17 for cooling cooling water and a pump 18. The compressor bodies 12 and 13 are cooled through the cooling jackets 15 and 16. There is still further provided a lubricating oil circulating flowpassage 25 which extends from an oil tank 20 via an oil pump 21, an air heat exchanger 22 for cooling lubricating oil and an oil filter 23 to lubricating oil supplied parts such as the gear box 14, a bearing and a shaft seal part not shown and returning to the oil tank 20, cooled lubricating oil being supplied to said lubricating oil supplied parts.
In the aforementioned conventional apparatus, the compressor bodies 12 and 13 are cooled by cooling water.
On the other hand, there are some users who cannot secure cooling water. For such users, there is considered an apparatus which circulates lubricating oil instead of water in the cooling water circulating flowpassage 19.
However, the apparatus having the aforementioned configuration has a problem in that two separate and independent flowpassages for circulating the same lubricating oil are to be provided, two pumps for delivering lubricating oil are required, and consuming power through an amount for the increased number thereof increases.
The present invention has been achieved to overcome the aforesaid problem encountered in prior art, and provides an air-cooled oil-free screw compressor which is simple in construction and enables reduction of consuming power.